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<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>
  <script>

    const x = "-10";
    const y = 4;
    // +x => Number(x)
    console.log(+x + y); // -6
    console.log(Number(x) + y); // -6

  </script>
</body>

</html>